principles of epidemiologyin public health practice_part5 docx

Public Health Surveillance Page 5-9 is an example where the syndrome is monitored as a proxy for the disease, and the syndrome is infrequent and severe enough to warrant investigation o

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Public Health Surveillance

Page 5-9

is an example where the syndrome is monitored as a proxy for the disease, and the syndrome is infrequent and severe enough to warrant investigation of each identified case

The goal of syndromic surveillance is to provide an earlier

indication of an unusual increase in illnesses than traditional

surveillance might, to facilitate early intervention (e.g., vaccination

or chemoprophylaxis) For syndromic surveillance, a syndrome is a constellation of signs and symptoms Signs and symptoms are grouped into syndrome categories (e.g., the category of

“respiratory” includes cough, shortness of breath, difficulty

breathing, and so forth)

The term, as used in the United States, often refers to observing emergency department visits for multiple syndromes (e.g.,

“respiratory disease with fever”) as an early detection system for a biologic or chemical terrorism event The advantage of syndromic surveillance is that persons can be identified when they seek

medical attention, which is often 1–2 days before a diagnosis is made In addition, syndromic surveillance does not rely on a

clinician’s ability to think of and test for a specific disease or on the availability of local laboratory or other diagnostic resources Because syndromic surveillance focuses on syndromes instead of diagnoses and suspect diagnoses, it is less specific and more likely

to identify multiple persons without the disease of interest As a result, more data have to be handled, and the analyses tend to be more complex Syndromic surveillance relies on computer

methods to look for deviations above baseline (certain methods look for space-time clusters) Emergency department data are the most common data source for syndromic surveillance systems You might use syndromic surveillance when:

• Timeliness is key either for naturally occurring infectious diseases (e.g., severe acute respiratory syndrome [SARS]),

or a terrorism event;

• Making a diagnosis is difficult or time-consuming (e.g., a new, emerging, or rare pathogen);

• Trying to detect outbreaks (e.g., when syndromic

surveillance identified an increase in gastroenteritis after a widespread electrical blackout, probably from consuming spoiled food); or

• Defining the scope of an outbreak (e.g., investigators

quickly having information on the age breakdown of patients or being able to determine geographic clustering) Syndromic surveillance is a key adjunct reporting system that can detect terrorism events early Syndromic surveillance is not

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intended to replace traditional surveillance, but rather to supplement it However, evaluation of these approaches is needed because syndromic surveillance is largely untested (fortunately, no terrorism events have occurred that test the available models); its usefulness has not been proven, given the early stage of the science and the relative lack of specificity of the systems Criticism and concern have arisen regarding the associated costs and the number

of false alarms that will be fruitlessly pursued and whether syndromic surveillance will work to detect outbreaks (See below for a possible scenario)

Possible Scenario for Syndromic Surveillance

Consider the time sequence of an unsuspecting person exposed to an aerosolized agent (e.g., anthrax)

• Two days after exposure, the person experiences a prodrome of headache and fever and visits a local pharmacy to buy acetaminophen or another over-the-counter medicine

• On day 3, he develops a cough and calls his health-care provider

• On day 4, feeling worse, he visits his physician’s office and receives a diagnosis of influenza

• On day 5, he feels weaker, calls 9-1-1, and is taken by ambulance to his local hospital’s emergency department, but is then sent home

• By day 6, he is admitted to the hospital with a diagnosis of pneumonia

• The following day, the radiologist identifies the characteristic feature of pulmonary anthrax on the chest radiograph and indicates a diagnosis Laboratory tests are also positive The infection-control practitioner, familiar with notifiable disease reporting, immediately calls the health department, which is on day 7 after exposure

Thus, the health department learns about this case and perhaps others a full 7 days after exposure However, if enough persons had been exposed on day 0, the health department might have detected an increase days earlier by using a syndromic surveillance system that tracks pharmacy over-the-counter medicine sales, nurses’ hotlines, managed care office visits, school or work absenteeism, ambulance dispatches, emergency medical system or 9-1-1 calls, or emergency room visits.

After a case definition has been developed, the persons conducting surveillance should determine the specific information needed from surveillance to implement control measures For example, the geographic distribution of a health problem at the county level might be sufficient to identify counties to be targeted for control measures, whereas the names and addresses of persons affected with sexually transmitted diseases are needed to identify contacts for follow-up investigation and treatment How quickly this information must be available for effective control is also critical

in planning surveillance For example, knowing of new cases of hepatitis A within a week of diagnosis is helpful in preventing further spread, but knowing of new cases of colon cancer within a year might be sufficient for tracking its long-term trend and the effectiveness of prevention strategies and treatment regimens

Another key component of establishing surveillance for a health problem is defining the scope of surveillance, including the geographic area and population to be covered by surveillance This is trial version

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Establishing a period during which surveillance initially will be conducted is also useful At the end of this period, the results of surveillance can be reviewed to determine whether surveillance should be continued This approach might prevent the continuation

of surveillance when it is no longer needed

Identifying or Collecting Data for Surveillance

After the problem for surveillance has been identified and defined and the needs and scope determined, available reports and other relevant data should be located that can be used to conduct surveillance These reports and data are gathered for different purposes from multiple sources by using selected methods Data might be collected initially to serve health-related purposes, whereas data might later serve administrative, legal, political, or economic purposes Examples of the former include collecting data from death certificates regarding the cause and circumstances of death and collecting data from national health surveys regarding health-related behaviors; examples of the latter include collecting data on cigarette and alcohol sales and administrative data

generated from the reimbursement of health-care providers

Before describing available local and national data resources for surveillance, understanding the principal sources and methods of obtaining data about health problems is helpful As you recall from Lesson 1, the majority of diseases have a characteristic natural history An understanding of the natural history of a disease is critical to conducting surveillance for that disease because someone — either the patient or a health-care provider — must recognize, or diagnose, the disease and create a record of its existence for it to be identified and counted for surveillance For diseases that cause severe illness or death (e.g., lung cancer or rabies), the likelihood that the disease will be diagnosed and recorded by a health-care provider is high For diseases that produce limited or no symptoms in the majority of those affected, the likelihood that the disease will be recognized is low Certain diseases fall between these extremes The characteristics and natural history of a disease determine how best to conduct surveillance for that disease

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• Receipts for cigarette and

other tobacco product sales

• Automated reports of

pharmaceutical sales

• Electronic records of billing

and payment for health-care

services

• Laws and regulations related

to drug use

Sources and Methods for Gathering Data

Data collected for health-related purposes typically come from three sources, individual persons, the environment, and health-care providers and facilities Moreover, data collected for nonhealth–related purposes (e.g., taxes, sales, or administrative data) might also be used for surveillance of health-related problems Because a researcher might wish to calculate rates of disease, information about the size of the population under surveillance and its geographic distribution are also helpful Table 5.2 summarizes health and nonhealth-related sources of data, and the box to the left provides examples of nonhealth-related data that can be used for surveillance of specific health problems

Table 5.2 Typical Sources of Data

Individual Persons Health-care providers, facilities, and records

— Air

— Water

— Animal vectors Administrative actions Financial transactions

— Sales of goods and services

— Taxation Legal actions Laws and regulations

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• Cities and towns monitor

public water supplies for

bacterial and chemical

contaminants

• State and local health

authorities monitor beaches,

lakes, and swimming pools

for increased levels of

harmful bacteria and other

biologic and chemical

hazards

• Health agencies monitor

animal and insect vectors for

the presence of viruses and

parasites that are harmful to

humans

• National, state, and local

departments of

transportation monitor roads,

highways, and bridges to

ensure that they are safe for

traffic; they also monitor

traffic to ensure that speed

limits and other traffic laws

are observed

• Public safety and health

departments periodically

monitor compliance with

laws requiring seat belt use

• Occupational health

authorities monitor noise

levels in the workplace to

prevent hearing loss among

employees

A limited number of methods are used to collect the majority of health-related data, including environmental monitoring, surveys, notifications, and registries These methods can be further

characterized by the approach used to obtain information from the sources described previously For example, the method of

collecting information might be an annual population survey that uses an in-person interview and a standardized questionnaire for obtaining data from women aged 18–45 years; or the method might

be a notification that requires completion and submission of a form

by health-care providers about occurrences of specific diseases that they see in their practices

Depending on the situation, these methods might be used to obtain information about a sample of a population or events or about all members of the population or all occurrences of a specific event (e.g., birth or death) Information might be collected continuously, periodically, or for a defined period, depending on the need

Careful consideration of the objectives of surveillance for a particular disease and a thorough understanding of the advantages and disadvantages of different sources and methods for gathering data are critical in deciding what data are needed for surveillance and the most appropriate sources and methods for obtaining it.9,14

We now discuss each of these four methods

Environmental Monitoring

Monitoring the environment is critical for ensuring that it is healthy and safe (see Examples of Environmental Monitoring) Multiple qualitative and quantitative approaches are used to monitor the environment, depending on the problem, setting, and planned use of the monitoring data

Survey

A survey is an investigation that uses a “structured and systematic gathering of information” from a sample of “a population of interest to describe the population in quantitative terms.”15 The majority of surveys gather information from a representative sample of a population so that the results of the survey can be generalized to the entire population Surveys are probably the most common method used for gathering information about populations The subjects of a survey can be members of the general public, patients, health-care providers, or organizations Although their topics might vary widely, surveys are typically designed to obtain specific information about a population and can be conducted once

or on a periodic basis

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Notification

A notification is the reporting of certain diseases or other related conditions by a specific group, as specified by law, regulation, or agreement Notifications are typically made to the state or local health agency Notifications are often used for surveillance, and they aid in the timely control of specific health problems or hazardous conditions When reporting is required by law, the diseases or conditions to be reported are known as

health-notifiable diseases or conditions

Individual notifiable disease case reports are considered confidential and are not available for public inspection In most states, a case report from a physician or hospital is sent to the local health department, which has primary responsibility for taking appropriate action The local health department then forwards a copy of the case report to the state health department In states that have no local health departments or in which the state heath

department has primary responsibility for collecting and investigating case reports, initial case reports go directly to the state health department In some states all laboratory reports are sent to the state health department, which informs the local health department responsible for following up with the physician

This form of data collection, in which health-care providers send reports to a health department on the basis of a known set of rules

and regulations, is called passive surveillance (provider-initiated)

Less commonly, health department staff may contact healthcare

providers to solicit reports This active surveillance (health

department- initiated) is usually limited to specific diseases over a limited period of time, such as after a community exposure or during an outbreak

Table 5.3 shows the types of notification and examples

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Table 5.3 Types of Notification and Examples

1 Disease or hazard-specific notifications

iii Provincial, state, or subnational: for example, coccidioidomycosis in California

b Chemical and physical hazards in the environment

i Childhood lead poisoning

ii Occupational hazards

iii Firearm-related injury

iv Consumer product-related injury

2 Notifications related to treatment administration

a Adverse effect of drugs or medical products

b Adverse effect from vaccines

3 Notifications related to persons at risk

a Elevated blood lead among adults

b Elevated blood lead among children

Adapted from: Koo D, Wingo P, Rothwell C Health Statistics from Notifications, Registration Systems, and Registries In: Friedman

D, Parrish RG, Hunter E (editors) Health Statistics: Shaping Policy and Practice to Improve the Population’s Health New York: Oxford University Press; 2005, p 82

Use of sentinel sites has

become the preferred approach

for human immunodeficiency

virus/acquired

immunodeficiency syndrome

(HIV/AIDS) surveillance for

certain countries where

national population-based

surveillance for HIV infection is

not feasible This approach is

based on periodic serologic

surveys conducted at selected

sites with well-defined

population subgroups (e.g.,

prenatal clinics) Under this

strategy, health officials define

the population subgroups and

the regions to study and then

identify health-care facilities

serving those populations that

are capable and willing to

participate These facilities

then conduct serologic surveys

at least annually to provide

statistically valid estimates of

HIV prevalence

Because underreporting is common for certain diseases, an

alternative to traditional reporting is sentinel reporting, which

relies on a prearranged sample of health-care providers who agree

to report all cases of certain conditions These sentinel providers are clinics, hospitals, or physicians who are likely to observe cases

of the condition of interest The network of physicians reporting influenza-like illness, as described in one of the examples in Appendix C,is an example of surveillance that uses sentinel providers Although the sample used in sentinel surveillance might not be representative of the entire population, reporting is probably consistent over time because the sample is stable and the

participants are committed to providing high-quality data

Registries

Maintaining registries is a method for documenting or tracking events or persons over time (Table 5.4) Certain registries are required by law (e.g., registries of vital events) Although similar

to notifications, registries are more specific because they are intended to be a permanent record of persons or events For example, birth and death certificates are permanent legal records that also contain important health-related information A disease registry (e.g., a cancer registry) tracks a person with disease over time and usually includes diagnostic, treatment, and outcome information Although the majority of disease registries require health facilities to report information on patients with disease, an active component might exist in which the registry periodically updates patient information through review of health, vital, or other records

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Reanalysis or Secondary Use of Data

Surveillance for a health problem can use data originally collected for other purposes — a practice known as the reanalysis or

secondary use of data This approach is efficient but can suffer from a lack of timeliness, or it can lack sufficient detail to address the problem under surveillance Because the primary collection of data for surveillance is time-consuming and resource-intensive if done well, it should be undertaken only if the health problem is of high priority and no other adequate source of data exists

Table 5.4 Types of Registries and Examples of Selected Types

1 Vital event registration

b Registries of persons at risk for selected conditions

c Registries of persons positive for genetic conditions

3 Disease-specific registries

a Blind registries

b Birth defects registries

c Cancer registries

d Psychiatric case registries

e Ischemic heart disease registries

6 Registries of persons at risk or exposed

a Children at high risk for developing a health problem

b Occupational hazards registries

c Medical hazards registries

d Older persons or chronically ill registries

e Atomic bomb survivors (Japan)

f World Trade Center survivors (New York City)

7 Skills and resources registries

8 Prospective research studies

9 Specific information registries

Adapted from: Koo D, Wingo P, Rothwell C Health Statistics from Notifications, Registration Systems, and Registries In: Friedman D, Parrish RG, Hunter E (editors) Health Statistics: Shaping Policy and Practice to Improve the Population’s Health New York: Oxford University Press; 2005, p 91

Weddell JM Registers and registries: a review Int J Epid 1973;2:221–8

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Exercise 5.2

State funding for a childhood asthma program has just become available

To initiate surveillance for childhood asthma, the staff is reviewing different sources of data on asthma Discuss the advantages and disadvantages of the following sources of data and methods for conducting surveillance for asthma (Figure 5.12 in Appendix C indicates national data for these different sources.)

• Self-reported asthma prevalence and asthmatic attacks obtained by a telephone survey

of the general population

• Asthma-associated outpatient visits obtained from periodic surveys of local health-care providers, including emergency departments and hospital outpatient clinics

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Major health data systems

Data regarding the characteristics of diseases and injuries are critical for guiding efforts for preventing and controlling those diseases Multiple systems exist in the United States to gather such data, as well as other health-related data, at national, state, and local levels These systems provide the “morbidity and mortality reports and other relevant data” for surveillance, as described by Langmuir, and examples of such systems are listed in Appendix E Remember, however, that surveillance is an activity — the

continued watchfulness over a disease by using data collected about it — and not the data about a disease or the different data systems used to collect or manage such data

Surveillance for communicable diseases principally relies upon reports of notifiable diseases from health-care providers and laboratories and the registration of deaths Because the most common use of surveillance for communicable diseases at the local level is to prevent or control cases of disease, local surveillance relies on finding individual cases of disease through notifications

or, where more complete reporting is required, actively contacting health-care facilities or providers on a regular basis.10 At the state and national level, the principal notification system in the United States is the National Notifiable Disease Surveillance System (NNDSS) State and local vital registration provides data for monitoring deaths from certain infectious diseases (e.g., influenza and AIDS)

More About the National Notifiable Disease Surveillance System

A notifiable disease is one for which regular, frequent, and timely information regarding individual cases is considered necessary for preventing and controlling the disease

The list of nationally notifiable diseases is revised periodically For example, a disease might be added to the list as a new pathogen emerges, and diseases are deleted as incidence declines Public health officials at state health

departments and CDC collaborate in determining which diseases should be nationally notifiable The Council of State and Territorial Epidemiologists, with input from CDC, makes recommendations annually for additions and deletions However, reporting of nationally notifiable diseases to CDC by the states is voluntary Reporting is mandated (i.e., by legislation or regulation) only at the state and local levels Thus, the list of diseases considered notifiable varies slightly by state All states typically report diseases for which the patients must be quarantined (i.e., cholera, plague, and yellow fever) in compliance with the World Health Organization's International Health Regulations

Data in the National Notifiable Disease Surveillance System (NNDSS) are derived primarily from reports transmitted

to CDC by the 50 states, two cities, and five territorial health departments

Source: National Notifiable Diseases Surveillance System [Internet] Atlanta: CDC [updated 2006 Jan 13] Available from:

http://www.cdc.gov/epo/dphsi/nndsshis.htm

Surveillance for chronic diseases usually relies upon health-care–This is trial version

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Surveillance for behaviors that influence health and for other markers for health (e.g., smoking, blood pressure, and serum cholesterol) is accomplished by population surveys, which might

be supplemented with health-care related data The Behavioral Risk Factor Surveillance System (BRFSS), the Youth Risk

Behavior Surveillance System (YRBSS), the National Health Interview Survey (NHIS), and the National Household Survey on Drug Abuse are all surveys that gather data regarding behaviors that influence health The National Health and Nutrition

Examination Survey (NHANES), probably the most

comprehensive survey in the United States of health and the factors that influence it, gathers extensive data on physiologic and

biochemical measures of the population and on the presence of chemicals among the population resulting from environmental exposures (e.g., lead, pesticides, and cotinine from secondhand smoke).Data from NHANES have been used for approximately 40 years to monitor the lead burden among the general public,

demonstrating its marked elevation and then substantial decline after the mandated removal of lead from gasoline and paint

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Exercise 5.3

Assume you work in a state in which none of the following conditions is

on the state list of notifiable diseases For each condition, list at least one existing source of data that you need for conducting surveillance on the condition What factors make the selected source or data system more appropriate than another?

Listeriosis: A serious infection can result from eating food contaminated with the bacterium

Listeria monocytogenes The disease affects primarily pregnant women, newborns, and adults

with weakened immune systems A person with listeriosis has fever, muscle aches, and

sometimes gastrointestinal symptoms (e.g., nausea or diarrhea) If infection spreads to the nervous system, such symptoms as headache, stiff neck, confusion, loss of balance, or

convulsions can occur Infected pregnant women might experience only a mild influenza-like illness; however, infections during pregnancy can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn In the United States, approximately 800 cases of

listeriosis are reported each year Of those with serious illness, 15% die; newborns and

immunocompromised persons are at greatest risk for serious illness and death

Spinal cord injury: Approximately 11,000 persons sustain a spinal cord injury (SCI) each year

in the United States, and 200,000 persons in the United States live with a disability related to

an SCI More than half of the persons who sustain SCIs are aged 15–29 years The leading cause of SCI varies by age Motor vehicle crashes are the leading cause of SCIs among persons aged <65 years Among persons aged ≥65 years, falls cause the majority of spinal cord

injuries Sports and recreation activities cause an estimated 18% of spinal cord injuries

Lung cancer among nonsmokers: A usually fatal cancer of the lung can occur in a person who

has never smoked An estimated 10%–15% of lung cancer cases occur among nonsmokers, and this type of cancer appears to be more common among women and persons of East Asian ancestry

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Analyzing and Interpreting Data

After morbidity, mortality, and other relevant data about a health problem have been gathered and compiled, the data should be

analyzed by time, place, and person Different types of data are

used for surveillance, and different types of analyses might be needed for each For example, data on individual cases of disease are analyzed differently than data aggregated from multiple

records; data received as text must be sorted, categorized, and coded for statistical analysis; and data from surveys might need to

be weighted to produce valid estimates for sampled populations For analysis of the majority of surveillance data, descriptive

methods are usually appropriate The display of frequencies

(counts) or rates of the health problem in simple tables and graphs,

as discussed in Lesson 4, is the most common method of analyzing data for surveillance Rates are useful — and frequently preferred

— for comparing occurrence of disease for different geographic areas or periods because they take into account the size of the population from which the cases arose One critical step before calculating a rate is constructing a denominator from appropriate population data For state- or countywide rates, general population data are used These data are available from the U.S Census

Bureau or from a state planning agency For other calculations, the population at risk can dictate an alternative denominator For example, an infant mortality rate uses the number of live-born infants; rates of surgical wound infections in a hospital requires the number of such procedures performed In addition to calculating frequencies and rates, more sophisticated methods (e.g., space-time cluster analysis, time series analysis, or computer mapping) can be applied

To determine whether the incidence or prevalence of a health problem has increased, data must be compared either over time or across areas The selection of data for comparison depends on the health problem under surveillance and what is known about its typical temporal and geographic patterns of occurrence

For example, data for diseases that indicate a seasonal pattern (e.g., influenza and mosquito-borne diseases) are usually compared with data for the corresponding season from past years Data for

diseases without a seasonal pattern are commonly compared with data for previous weeks, months, or years, depending on the nature

of the disease Surveillance for chronic diseases typically requires data covering multiple years Data for acute infectious diseases might only require data covering weeks or months, although data extending over multiple years can also be helpful in the analysis of This is trial version

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the natural history of disease Data from one geographic area are sometimes compared with data from another area For example, data from a county might be compared with data from adjacent counties or with data from the state We now describe common methods for, and provide examples of, the analysis of data by time, place, and person

Analyzing by time

Basic analysis of surveillance data by time is usually conducted to characterize trends and detect changes in disease incidence For notifiable diseases, the first analysis is usually a comparison of the number of case reports received for the current week with the number received in the preceding weeks These data can be

organized into a table, a graph, or both (Table 5.5 and Figures 5.2 and 5.3) An abrupt increase or a gradual buildup in the number of cases can be detected by looking at the table or graph For

example, health officials reviewing the data for Clark County in Table 5.5 and Figures 5.2 and 5.3 will have noticed that the

number of cases of hepatitis A reported during week 4 exceeded the numbers in the previous weeks This method works well when new cases are reported promptly

Table 5.5 Reported Cases of Hepatitis A, by County and Week of

Report, 1991

Week of report County

County during weeks 1–4 during 1991 exceeded the numbers reported during the same 4-week period during the previous 3 years A related method involves comparing the cumulative

number of cases reported to date during the current year (or during the previous 52 weeks) to the cumulative number reported to the same date during previous years

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Table 5.6 Reported Cases of Hepatitis A, by County for Weeks 1–4, 1988–1991

Year County

Analysis of long-term time trends, also known as secular trends,

usually involves graphing occurrence of disease by year Figure 5.1 illustrates the rate of reported cases of malaria for the United States during 1932–2003 Graphs can also indicate the occurrence

of events thought to have an impact on the secular trend (e.g., implementation or cessation of a control program or a change in the method of conducting surveillance) Figure 5.2 illustrates reported morbidity from malaria for 1932–1962, along with events and control activities that influenced its incidence.2

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Adapted from: Centers for Disease Control and Prevention Summary of notifiable diseases, United States, 1993b MMWR

1993;42(53):38

Langmuir AD The surveillance of communicable diseases of national importance N Engl J Med 1963;268:182–92

Figure 5.2 Reported Malaria Morbidity in the United States, 1932–1962

Langmuir AD The surveillance of communicable diseases of national importance N Engl J Med 1963;268:184.

TVA MALARIA CONTROL PROGRAM Water management, antilarval, and antimaginal

WPA MALARIA CONTROL DRAINAGE PROGRAM

Antilarval measures

WAR AREAS PROGRAM

To protect military trainees from malaria — antilarval measures

EXTENDED PROGRAM

To prevent spread of malaria from returning troops — DDT

MALARIA ERADICATION PROGRAM DDT and treatment MALARIA SURVEILLANCE AND PREVENTION PRIMAQUINE Treatment of servicemen

on transports returning from malaria-endemic areas

Relapses from Korea

Relapses from overseas cases

Probable effect of economic depression

Figure 5.1 Rate (per 100,000 Persons) of Reported Cases of Malaria, By Year, United States, 1932–

Period included in Figure 5.5

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Statistical methods can be used to detect changes in disease occurrence The Early Aberration Detection System (EARS) is a package of statistical analysis programs for detecting aberrations or deviations from the baseline, by using either long- (3–5 years) or short-term (as short as 1–6 days) baselines.16

Figure 5.3 Age-Adjusted Lung and Bronchus Cancer Mortality Rates (per 100,000 Population) By State

choropleth, maps to much more sophisticated applications.17

Using GIS is particularly effective when different types of information about place are combined to identify or clarify geographic relationships For example, in Figure 5.4, the absence This is trial version

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or presence of the tick that transmits Lyme disease, Ixodes

scapularis, are illustrated superimposed over habitat suitability.18

Such software packages as SatScan™ (Martin Kulldorff, Harvard University and Information Management System, Inc., Silver Spring, Maryland), EpiInfo™ (CDC, Atlanta, Georgia), and Health Mapper (World Health Organization, Geneva, Switzerland)

provide GIS functionality and can be useful when analyzing surveillance data.19-21

Figure 5.4 Predictive Risk Map of Habitat Suitability for Ixodes scapularis in Wisconsin and Illinois

Source: Guerra M, Walker E, Jones C, Paskewitz S, Cortinas MR, Stancil A, Beck L, Bobo M, Kitron U Predicting the risk of Lyme disease: habitat suitability for Ixodes scapularis in the north central United States Emerg Infect Dis 2002;8:289–97

Analyzing by time and place

As a practical matter, disease occurrence is often analyzed by time and place simultaneously An analysis by time and place can be organized and presented in a table or in a series of maps

highlighting different periods or populations (Figures 5.5 and 5.6)

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Figure 5.5 Age-Adjusted Colon Cancer Mortality Rates* for White Females by State — United States, 1950–1954, 1970–1974, and 1990–1994

*Scale based on 1950–1994 rates (per 100,000 person years)

Data Source: Customizable Mortality Maps [Internet] Bethesda: National Cancer Institute [cited 2006 Mar 22] Available from:

http://cancercontrolplanet.cancer.gov/atlas/index.jsp

Figure 5.6 Age-Adjusted Colon Cancer Mortality Rates* for White Males by State — United States, 1950–1954, 1970–1974, and 1990–1994

*Scale based on 1950–1994 rates (per 100,000 person years)

Data Source: Customizable Mortality Maps [Internet] Bethesda: National Cancer Institute [cited 2006 Mar 22] Available from: http://cancercontrolplanet.cancer.gov/atlas/index.jsp

Age

Meaningful age categories for analysis depend on the disease of interest Categories should be mutually exclusive and all-inclusive Mutually exclusive means the end of one category cannot overlap with the beginning of the next category (e.g., 1–4 years and 5–9 years rather than 1–5 and 5–9) All-inclusive means that the categories should include all possibilities, including the extremes This is trial version

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of age (e.g., <1 year and ≥84 years) and unknowns

Standard age categories for childhood illnesses are usually <1 year and ages 1–4, 5–9, 10–14, 15–19, and ≥20 years For pneumonia and influenza mortality, which usually disproportionally affects older persons, the standard categories are <1 year and 1–24, 25–44, 45–64, and ≥65 years Because two-thirds of all deaths in the United States occur among persons aged ≥65 years, researchers often divide the last category into ages 65–74, 75–84, and ≥85 years

The characteristic age distribution of a disease should be used in deciding the age categories — multiple narrow categories for the peak ages, broader categories for the remainder If the age

distribution changes over time or differs geographically, the

categories can be modified to accommodate those differences

To use data in the calculation of rates, the age categories must be consistent with the age categories available for the population at risk For example, census data are usually published as <5 years, 5–9, 10–14, and so on in 5-year age groups These denominators could not be used if the surveillance data had been categorized in different 5-year age groups (e.g., 1–5 years, 6–10, 11–15, and so forth)

Other Person- or Disease-Related Risk Factor

For certain diseases, information on other specific risk factors (e.g., race, ethnicity, and occupation) are routinely collected and regularly analyzed For example, have any of the reported cases of hepatitis A occurred among food-handlers who might expose (or might have exposed) unsuspecting patrons? For hepatitis B case reports, have two or more reports listed the same dentist as a potential source? For a varicella (chickenpox) case report, had the patient been vaccinated? Analysis of risk-factor data can provide information useful for disease control and prevention

Unfortunately, data regarding risk factors are often not available for analysis, particularly if a generic form (i.e., one report form for all diseases) or a secondary data source is used

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Interpreting results of analyses

When the incidence of a disease increases or its pattern among a specific population at a particular time and place varies from its expected pattern, further investigation or increased emphasis on prevention or control measures is usually indicated The amount of increase or variation required for action is usually determined locally and reflects the priorities assigned to different diseases, the local health department’s capabilities and resources, and

sometimes, public, political, or media attention or pressure

For certain diseases (e.g., botulism), a single case of an illness of public health importance or suspicion of a common source of infection for two or more cases is often sufficient reason for

initiating an investigation Suspicion might also be aroused from finding that patients have something in common (e.g., place of residence, school, occupation, racial/ethnic background, or time of onset of illness) Or a physician or other knowledgeable person might report that multiple current or recent cases of the same disease have been observed and are suspected of being related (e.g., a report of multiple cases of hepatitis A within the past 2 weeks from one county)

Observed increases or decreases in incidence or prevalence might, however, be the result of an aspect of the way in which

surveillance was conducted rather than a true change in disease occurrence Common causes of such artifactual changes are:

• Changes in local reporting procedures or policies (e.g., a change from passive to active surveillance)

• Changes in case definition (e.g., AIDS in 1993)

• Increased health-seeking behavior (e.g., media publicity

prompts persons with symptoms to seek medical care)

• Increase in diagnosis

• New laboratory test or diagnostic procedure

• Increased physician awareness of the condition, or a new

of January during the second week of January)

www.adultpdf.com

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Page 5-30

Artifactual changes include an increase in population size, improved diagnostic procedures, enhanced reporting, and duplicate reporting Compare the sharp increases in disease incidence

illustrated in Figures 5.7 and 5.8 Although they appear similar, the increase displayed in Figure 5.7 represents a true increase in incidence, whereas the increase displayed in Figure 5.8 resulted from a change in the case definition.22,23 Nonetheless, because a health department’s primary responsibility is to protect the health

of the public, public health officials usually consider an apparent increase real, and respond accordingly, until proven otherwise

Figure 5.7 Reported Cases of Salmonellosis per

100,000 Population, By Year — United States,

1972–2002

Source: Centers for Disease Control and Prevention

Summary of notifiable diseases–United States, 2002

Published April 30, 2004, for MMWR 2002;51(No 53): p 59

Figure 5.8 Reported Cases of AIDS, by Year — United States* and U.S Territories, 1982–

2002

* Total number of AIDS cases includes all cases reported to CDC as of December 31, 2002 Total includes cases among residents in the U.S territories and 94 cases among persons with unknown state of residence

Source: Centers for Disease Control and Prevention Summary of notifiable diseases–United States, 2002 Published April 30, 2004, for MMWR 2002;51(No 53): p

59

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Page 5-31

Exercise 5.4

During the previous 6 years, one to three cases per year of tuberculosis had been reported to a state health department During the past 3 months, 17 cases have been reported All but two of these cases have been reported from one county The local newspaper published an article about one of the first reported cases, which occurred in a girl aged 3 years Describe the possible causes of the increase in reported cases

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Page 5-32

“Development of a reasonably

effective primary surveillance

system took time Usually, 2

full years were required

Experience showed that

development was best

achieved by establishing for

each administrative unit of

perhaps 2–5 million

population, a surveillance

team of perhaps two to four

persons with transport Each

team, in addition to its other

duties in outbreak

containment, visited each

reporting unit regularly to

explain and discuss the

program, to distribute forms

(and often vaccine), and to

check on those who were

delinquent in reporting

Regularly distributed

surveillance reports also

helped to motivate these

units Undoubtedly, the

greatest stimulus to reporting

was the prompt visit of the

surveillance team for outbreak

investigations and control

whenever cases were

reported This simple,

obvious, and direct indication

that the routine weekly

reports were actually seen

and were a cause for public

health action did more, I am

sure, than the multitude of

government directives which

were issued ” [Emphasis

added] 25

Disseminating Data and Interpretations

As Langmuir2 emphasized, the timely, regular dissemination of basic data and their interpretations is a critical component of surveillance Data and interpretations should be sent to those who provided reports or other data (e.g., health-care providers and laboratory directors) They should also be sent to those who use them for planning or managing control programs, administrative purposes, or other health-related decision-making

Dissemination of surveillance information can take different forms Perhaps the most common is a surveillance report or summary, which serves two purposes: to inform and to motivate Information

on the occurrence of health problems by time, place, and person informs local physicians about their risk for their encountering the problem among their patients Other useful information

accompanying surveillance data might include prevention and control strategies and summaries of investigations or other studies

of the health problem A report should be prepared on a regular basis and distributed by mail or e-mail and posted on the health department’s Internet or intranet site, as appropriate Increasingly, surveillance data are available in a form that can be queried by the general public on health departments’ Internet sites.24

A surveillance report can also be a strong motivational factor in that it demonstrates that the health department actually looks at the case reports that are submitted and acts on those reports Such efforts are important in maintaining a spirit of collaboration among the public health and medical communities, which in turn,

improves the reporting of diseases to health authorities

State and local health departments often publish a weekly or monthly newsletter that is distributed to the local medical and public health community These newsletters usually provide tables

of current surveillance data (e.g., the number of cases of disease identified since the last report for each disease and geographic area under surveillance), the number of cases previously identified (for comparison with current numbers), and other relevant information They also usually contain information of current interest about the prevention, diagnosis, and treatment of selected diseases and summarize current or recently completed epidemiologic investigations

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